1. Field of the Invention
The present invention relates to a magnetic detecting element including a pinned magnetic layer whose magnetization direction is fixed and a free magnetic layer which is formed on the pinned magnetic layer with a non-magnetic layer interposed therebetween and whose magnetization direction varies in accordance with an external magnetic field. In particular, the invention relates to a magnetic detecting element capable of maintaining large ΔRA, which is the product of a magnetoresistance variation ΔR and an element area A, and of reducing magnetostriction, and a method of manufacturing the same.
2. Description of the Related Art
A magnetic detecting element having a multi-layer film of a free magnetic layer, a non-magnetic layer, and a pinned magnetic layer is classified into a CIP (current in the plane) type or a CPP (current perpendicular to the plane) type, according to a direction in which a current flows through the multi-layer film.
In the CIP-type magnetic detecting element, a current flows in a direction parallel to the surface of each layer of the multi-layer film. In the CPP-type magnetic detecting element, a current flows in a direction perpendicular to the surface of each layer of the multi-layer film.
In general, the CPP-type magnetic detecting element has an advantage in that it has an element size smaller than that of the CIP-type magnetic detecting element to more increase reproduction power. Therefore, the CPP-type magnetic detecting element has a structure capable of achieving high-density recording, and thus it is expected that the CPP-type magnetic detecting element will be used in place of the currently dominating CIP-type magnetic detecting element in the near future.
Further, the free magnetic layer is formed of, for example, a CoFe alloy or an NiFe alloy. For example, JP-A-2004-282073 discloses the free magnetic layer formed of the CoFe alloy.
In addition, JP-A-2004-282073 discloses a method of controlling the magnetostriction of the free magnetic layer. In a structure disclosed in JP-A-2004-282073, the free magnetic layer includes a plurality of ferromagnetic layers formed of a CoFe alloy and copper layers provided among the ferromagnetic layers, and a copper layer subjected to an oxidation exposure process is included in the copper layers, which makes it possible to reduce the magnetostriction of the free magnetic layer.
However, since the CoFe alloy has higher uniaxial anisotropy and stronger coercive force than an NiFe alloy, the CoFe alloy, which is the main ingredient of the free magnetic layer, makes it difficult to invert the magnetization of the free magnetic layer with an external magnetic field, resulting in low sensitivity.
Further, in the structure disclosed in JP-A-2004-282073, the copper layer subjected to the oxidation exposure process is necessarily included in the free magnetic layer. However, since the copper layer is apt to oxidize, the CoFe alloy formed below the copper layer is also apt to oxidize, which causes serious problems in that the free magnetic layer is demagnetized and magnetic characteristics of the free magnetic layer are deteriorated.
It is possible to increase the value of ΔRA, which is the product of a magnetoresistance variation ΔR and an element area A by forming the free magnetic layer containing an NiFe alloy as the main ingredient and by appropriately adjusting the composition ratio of the NiFe alloy. An increase in the value of ΔRA is a very important factor to achieve a CPP-type magnetic detecting element having high recording density in the near future.
However, when the composition ratio of Ni in the NiFe alloy is adjusted to increase the value of ΔRA, the magnetostriction becomes large. The large magnetostriction causes problems in which a film is distorted and the free magnetic layer is much affected by stress caused by a difference between a thermal expansion coefficient thereof and thermal expansion coefficient of other layers. Therefore, it is necessary to reduce the magnetostriction of the free magnetic layer while maintaining large ΔRA.
Further, JP-A-2004-95587 discloses a structure in which a free magnetic layer is formed of an NiFe alloy. In the structure disclosed in JP-A-2004-95587, the free magnetic layer has a laminated ferrimagnetic structure of a first free magnetic layer, a non-magnetic intermediate layer, and a second free magnetic layer. The free magnetic layer is formed in a laminated structure of an NiFe film, an Ru film, and an NiFe film. An RKKY interaction occurs between the first free magnetic layer and the second free magnetic layer, which causes the magnetization direction of the first free magnetic layer to be antiparallel to that of the second free magnetic layer (see paragraph [0068] of JP-A-2004-95587).
However, an object of JP-A-2004-95587 is only to increase the value of ΔRA, but JP-A-2004-95587 does not disclose a structure for maintaining large ΔRA and for reducing magnetostriction when the free magnetic layer is formed of an NiFe alloy.